Engine Stop Control With Catalytic-Converter Oxygen Feedback
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Solution Overview
Problem
Conventional engine stop and restart systems in hybrid vehicles fail to account for the quantity of oxygen stored in the catalytic converter, leading to excessive oxygen storage that causes NOx emissions during restart.
Innovation Solution
Calculate the quantity of oxygen stored in the catalytic converter and adjust the enrichment amount based on this value to maintain it within a suitable range, reducing the oxygen before engine stop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If enrichment operation is performed to reduce stored oxygen in catalytic converter before engine stop, then NOx emissions at restart are reduced, but stored oxygen quantity may be excessively reduced
Solution Approach 1:
The control device calculates the stored oxygen quantity in the catalytic converter based on sensor signals and uses this calculated value as feedback to determine the appropriate enrichment amount. The enrichment operation is adjusted dynamically according to the actual stored oxygen level, preventing both excessive oxygen (which causes NOx emissions) and excessive reduction (which harms catalytic converter performance).
Solution Approach 2:
The control device changes the air-fuel ratio parameter during enrichment operation based on the calculated stored oxygen quantity. By adjusting the enrichment amount according to the stored oxygen level, the system optimizes the balance between reducing NOx emissions and maintaining sufficient oxygen storage for catalytic converter function.
2Loss of energy
If automatic stop and restart is repeated to improve fuel efficiency, then fuel consumption is reduced, but NOx emissions increase due to excessive oxygen storage
Solution Approach 1:
The control device performs preliminary enrichment operation before engine stop to reduce stored oxygen in the catalytic converter. This preliminary action ensures that when the engine restarts after idle stop, the oxygen level is optimized to prevent NOx emissions, allowing frequent stop-start cycles to be performed without increasing harmful emissions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents excessive reduction of stored oxygen, minimizing NOx emissions during engine restart by optimizing the enrichment operation.
Implementation Method 1
a quantity of oxygen stored in a catalytic converter is calculated while an engine is operating
Implementation Method 2
a quantity of oxygen stored in a catalytic converter is reduced by enriching an air fuel ratio immediately before the engine is stopped
Data Source
AI summary
In response to an engine temporary stop request, a quantity of oxygen stored in a catalytic converter is reduced by controlling an in-cylinder air fuel ratio to be richer than stoichiometric. The quantity of stored oxygen is calculated while the engine is operating. An amount of air fuel ratio enrichment is set based on the quantity of stored oxygen calculated when the stop request occurs, such that the amount of air fuel ratio enrichment decreases as the quantity of stored oxygen decreases. An opening of a throttle valve is reduced in response to the stop request. Engine stop is permitted when the reduction of the opening of the throttle valve causes an internal pressure of an intake passage downstream of the throttle valve to reach a predetermined negative pressure, and the air fuel ratio enrichment operation causes the quantity of stored oxygen to reach a predetermined target value.